1. Field of the Invention
The present invention relates to an image display device and adjustment method thereof.
2. Description of the Related Art
Heretofore, there have been disclosed projection-type image display devices including an illumination device, an optical modulator illuminated by the illumination device, and a projector lens for imaging the image of the optical modulator. These have employed as a light source a discharge lamp, and as an image modulator transmission-type liquid crystal display element (HTPS), reflection-type liquid crystal display element (LCOS), or digital micro-mirror device (DMD), and accordingly, devices and optical system have been improved variously.
The projection-type image display devices include a light source for emitting white light, separate the while light from the light source into three colors of red, green, and blue at a dichroic mirror, and illuminate an optical modulator corresponding to each color. Subsequently, after being modulated at the optical modulator, the optical beams are synthesized by a color synthesizer such as a cross prism or the like, and are projected on a screen by the projector lens.
The schematic configuration of a projection-type image display device according to the related art will be described with the schematic configuration diagram shown in FIG. 14. As shown in FIG. 14, with a projection-type image display device 101, a light emitting unit 112 of a light source 111 is disposed in the focal position of a reflector 113. The light emitted from this light source 111 is reflected off the reflector 113 to become generally parallel light, and is input to a first integrator lens 114 and second integrator lens 115. These lenses have an advantage for uniforming the illuminance of light lately input to an optical modulator 123. The light flux emitted from the second integrator lens 115 is input to a polarization beam splitter 116, where the light is subjected to polarization to obtain light in a predetermined polarization direction. The light emitted from the polarization beam splitter 116 is input and condensed in a condensing lens 117.
The white light emitted from the condensing lens 117 is separated by a dichroic mirror 118. For example, with the dichroic mirror 118, red wavelength band light is transmitted and green wavelength band light and blue wavelength band light are reflected. After being transmitted through a reflective mirror 119 and field lens 120 (120-1), the transmitted red wavelength band light is input to a reflection-type polarization element 121 (121-1), and illuminates an optical modulator 123 (reflection-type liquid crystal display element 123-1).
On the other hand, the light reflected off the dichroic mirror 118 is input to another dichroic mirror 124. With the dichroic mirror 124, the blue wavelength band light is transmitted, and the green wavelength band light is reflected. The separated light fluxes are input to field lenses 120 (120-2), 120 (120-3), reflection-type polarization element 121 (121-2), 121 (121-3), and illuminate optical modulator 123 (reflection-type liquid crystal display element 123-2), and optical modulator 123 (reflection-type liquid crystal display element 123-3), respectively.
Each color beam optically modulated at the optical modulator 123 is input to the reflection-type polarization element 121, and according to degree of modulation, a portion thereof is transmitted to return to the direction of the light source (light source 111), and a portion thereof is reflected to input to a color synthesizing prism 125. The color synthesizing prism 125 is configured such that the green wavelength band light is transmitted, and the blue wavelength band light is reflected. Subsequently, the light fluxes of the respective colors are synthesized and input to a projector lens 126, where the image thereof is enlarged to a predetermined scale factor and projected on a screen (not shown) (e.g., see PCT Japanese Translation Patent Publication No. 2003-506746).
With the optical modulator 123 which is a liquid crystal display element, in order to control the tilt direction of the liquid crystal at the time of applying voltage, a slight angular slope (pretilt) is commonly added to the direction of ±45 degrees as to the incident polarization axis of an optical beam even in a nonelectric field state. Therefore, as to light perpendicularly input to the liquid crystal display element of the optical modulator 123, the liquid crystal display element servers as a minute phase difference element of which the optical axis is 45 degrees. Accordingly, in general, an optical compensation element 122 is employed as an optical element for canceling out this minute phase difference.
Next, description will be made regarding displaying black gradation. In a case where normally black type liquid crystal is employed as the optical modulator 123, and also reflection-type liquid crystal display elements 123-1 through 123-3 are employed, the driving voltage of the liquid crystal becomes a relatively small value when displaying the black gradation side. Accordingly, it is ideal for the polarization state of light between polarization element (incident side), liquid crystal display element, and polarization element (emission side) to be unchangeable.
However, the polarization state of the actual light flux is disarranged due to the extinction ratio of the polarization element, birefringence at a glass material between the polarization element and liquid crystal display element, minute phase difference at the liquid crystal display element, or the like. Further, influence such as device property, heat characteristic, stress from peripheral components, or the like causes the liquid crystal display element to have uneven phase difference property within the plane thereof in some cases.
As described above, in a case where uneven phase difference property is caused within the plane, light fluxes input to the respective positions of the liquid crystal display element each have a different polarization state (elliptical polarization). Accordingly, the transmittance or reflectance when inputting to the polarization element again differs, and consequently, this is displayed as unevenness of brightness on the screen. In a case where unevenness of brightness occurs as to each optical beam of R, G, and B, this is also recognized as unevenness of chromaticity.